The present invention relates to a method to provide a management channel as described in the preamble of claim 1, a line terminator, a first network terminator card and a second network terminator card realizing the method as described in the preambles of claim 7, claim 8 and claim 9 and an access network as described in the preamble of claim 10.
Such a method to provide a management channel is already known in the art e.g. from the contribution of Italtel to the Full Service Access Network FSAN Requirements Specifications for xe2x80x9cManagement of Optical Network Terminationsxe2x80x9d from the 3rd of December 1997. This document clarifies the requirements for standardized management procedures of network terminations in a mixed Fiber To The Home FTTH and Fiber To The Cabinet FTTCa environment. The Access Node Management System needs to remotely and dynamically configure each Access Network element and access its status information in terms of fault and performance. As described on page 3 of this document, when an optical network unit has to be supported over the passive optical network and has to be fully configured, after completion of the ranging procedure, additional management configuration procedures have to be carried out. Such information, called hereafter management information, needs to be provided to an optical line terminator in order to enable the performance of management functions such as e.g. equipment deactivation, equipment fault reporting, user network interfaces, user network interface fault reporting, user network performance reporting, . . . . It has to be remarked that although in the cited document, as shown in the FIGURE of page 1, a distinction is made between an optical network terminator ONT and an optical network unit ONU, in the claims and this further description the terms are defined as follows: a network unit NU includes a termination of a network i.e. a network termination or a network terminator cord NTC. In an optical network such a network termination is called PON termination. Such a network unit NU supports e.g. one hundred customers or only one customer whereby in the latter case the integration of the network unit NU and the customer network terminator is called network terminator NT.
In order to transport the management information a management channel has to be provided and to be set up. On page 5 of the above document it is described to introduce in the Asynchronous Transfer Mode Passive Optical Network ATM-PON specification Transmission Convergence TC layer a Physical Layer Operation And Maintenance PLOAM message in order to activate a virtual channel connection as management communication channel between the optical line terminator and an optical network unit. It has to be remarked that Physical layer operation and maintenance cells PLOAM""s are broadcasted in the network in order to transfer operation and maintenance information like e.g. alarm indication signal or bit interleaved parity check. Such PLOAM cells are described in the ITU-T Recommendation 1.610.
An objector the present invention is to provide a method for providing a management channel for use in a tree like access network of the above known type but which method is suited in case of redundant network terminator cards i.e. an active network terminator card and a stand-by network terminator card which are both included in one network unit.
According to the invention, this object is achieved with the method to provide a management channel as described in claim 1, and with the line terminator, the first network terminator card and the second network terminator card which are realizing the method as described in claim 7, claim 8 and claim 9 and the access network as described in claim 10.
Indeed, it has to be remarked that, following the above mentioned method of providing a management channel which makes use of a PLOAM cell, as e.g. one of the last steps of the ranging procedure, the line terminator determines for each PON termination a management channel. A straightforward evolution of this method in a tree like network with the cascade connection of one common link i.e. the root and dedicated links i.e. the branches, and with redundant network terminator cards in one physical location i.e. in one network unit, is that the line terminator card determines for each PON termination a management channel. This means that a first management channel for the first network terminator card is determined and a second management channel for the second network terminator card is determined.
However, in the event when a first network terminator card being the active network terminator card becomes in-active, due to e.g. an internal failure or a failure in its dedicated link, and a second network terminator card being the stand-by network terminator card becomes active, extra control resources are required in the line terminator to switch over from one management channel to another one. Indeed, the control resources are required in order to select and to control the use of the extra management channel for the second network terminator card. Moreover, extra bandwidth resources for an extra management channel is required before the bandwidth of the first management channel from the previous management channel can be released.
Accordingly the basic idea of the present invention, when the second network terminator card is using, in the event when it becomes active, the same management channel as the first network terminator card was using before when it was active, no extra bandwidth is required for the transportation of the management information and no extra resources are required in the line terminator in order to recognize or to control the second management channel. This unique management channel for the network unit which includes both network terminator cards is called hereafter and in the claims the network unit management channel. This network unit management channel transports the management information which is in fact related to the network unit itself and which is common for both network terminator cards. Indeed this management information includes e.g. information related to the internal communication system between the network terminator cards and the line interface modules or status information concerning these line interface modules which are providing the links towards the customers. Hence, the method of the present invention is suited for redundant network terminator cards which are included in one network unit of a tree like access network.
Another characteristic feature of the present invention is that the identifier information concerning the network unit management channel is provided by the line terminator to the first network terminator card, not following the above described prior art method with PLOAM""s cells during one of the last ranging steps, but following a predefined metaprotocol and via a predefined metachannel. In this way, no intervention has to be made within a complicated procedure such as the ranging procedure e.g. delay ranging and power leveling, which makes use of already defined fields in the PLOAM cells. The network terminator card only has to know the references to this predefined metachannel which can e.g. be hard-coded. These references might be e.g. the virtual channel identifier and virtual path identifier of a point to multipoint ATM connection whereby a predefined requestxe2x80x94answer procedure can be implemented between the network unit and the line terminator. This is described in claim 2.
It has to be remarked that it is obvious to a person skilled in the art that the line terminator has to know the following information: which network terminator card is the active network terminator card, which network terminator card is stand-by for which active network terminator card and in which network unit are both network terminator cards included. A possible way to provide such reference information is to preconfigure the line terminator with the configuration of the network. However, such a method has the disadvantage that possible changes to the configuration of the network requires adaptations to this preconfiguration. Therefor an additional feature of the present invention is described in claim 3. Following this method the reference information is provided by the network terminator card to the line terminator at a convenient time e.g. when the first network terminator card included in the network unit becomes active for the first time.
Also a feature of the present invention is that the method further includes the step of determining a management protocol according to management protocol information provided by the first line terminator card to the line terminator. Indeed, it has to be explained that the different kinds of management protocols can be implemented between a network unit and a line terminator. Since the management protocol between a network terminator, as defined in one of the above paragraphs, and a line terminator is a management protocol towards only one customer network terminator, it is expected not to be a complicated management protocol whereby standardization of this management protocol is feasible. On the other hand, the management protocol between a network unit which supports substantially 100 hundred customers is often a proprietary management protocol. But furthermore, it is possible that a network unit is able to support e.g. one or more proprietary management protocols and a standard management protocol. In the event when an network terminator card included in a network units provides to the line terminator the information concerning the different management protocols it is able to support, the line terminator determines based upon this information which management protocol the network terminator card has to follow. This is described in claim 4.
Yet another feature of the present invention is that in stead of defining only for network terminator cards, i.e. for PON terminations, an unambiguous unique identification address called media access control address, also defining for a network unit which includes one or more redundant pairs of active and stand-by network terminator cards an unambiguous unique identification address. This unambiguous unique identification address is called the media access control address of the network unit. By determining this media address control address, also the network unit management channel can be unambiguously identified by the line terminator. This is described in claim 5.
Still a further feature of the present invention is the way how the second network terminator card becomes aware of the identifier information of the network unit management channel. Since the line terminator determines the network unit management channel, a possible way to provide this identifier information to the stand-by optical network terminator card is via the line terminator. Such an implementation requires control signals between the standby optical network terminator card and the line terminator before its becomes active. However, claim 6 describes that the identifier information is provided by the active i.e. the first network terminator card to the stand-by i.e. the second network terminator card, which enables a future use of the network unit management channel without the above disadvantage.
It should further be noticed that the term xe2x80x9cincludingxe2x80x9d, used in the claims, should not be interpreted as being limitative to the means listed thereafter. Thus, the scope of the expression xe2x80x9ca device including means A and Bxe2x80x9d should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Similarly, it is to be noted that the term xe2x80x9ccoupledxe2x80x9d, also used in the claims, should not be interpreted as being limitative to direct connections only. Thus, the scope of the expression xe2x80x9ca device A coupled to a device Bxe2x80x9d should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means .